Don't copy the QuicAckFrame into the QuicPacketGenerator. Protected by quic_dont_copy_acks.

net/quic/quic_received_packet_manager.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // Manages the packet entropy calculation for both sent and received packets
 // for a connection.
 
 #ifndef NET_QUIC_QUIC_RECEIVED_PACKET_MANAGER_H_
 #define NET_QUIC_QUIC_RECEIVED_PACKET_MANAGER_H_
 
@@ skipping 98 matching lines @@
                                     const QuicPacketHeader& header,
                                     QuicTime receipt_time);
 
   // Checks whether |packet_number| is missing and less than largest observed.
   virtual bool IsMissing(QuicPacketNumber packet_number);
 
   // Checks if we're still waiting for the packet with |packet_number|.
   virtual bool IsAwaitingPacket(QuicPacketNumber packet_number);
 
   // Update the |ack_frame| for an outgoing ack.
+  // TODO(ianswett): Deprecate with
+  // gfe2_reloadable_flag_quic_dont_copy_ack_frames.
   void UpdateReceivedPacketInfo(QuicAckFrame* ack_frame,
                                 QuicTime approximate_now);
 
+  // Retrieves a frame containing a QuicAckFrame.  The ack frame may not be
+  // changed outside QuicReceivedPacketManager and must be serialized before
+  // another packet is received, or it will change.
+  const QuicFrame GetUpdatedAckFrame(QuicTime approximate_now);
+
   // QuicReceivedEntropyHashCalculatorInterface
   // Called by QuicFramer, when the outgoing ack gets truncated, to recalculate
   // the received entropy hash for the truncated ack frame.
   QuicPacketEntropyHash EntropyHash(
       QuicPacketNumber packet_number) const override;
 
   // Updates internal state based on |stop_waiting|.
   virtual void UpdatePacketInformationSentByPeer(
       const QuicStopWaitingFrame& stop_waiting);
 
@@ skipping 46 matching lines @@
   QuicTime time_largest_observed_;
 
   QuicConnectionStats* stats_;
 
   DISALLOW_COPY_AND_ASSIGN(QuicReceivedPacketManager);
 };
 
 }  // namespace net
 
 #endif  // NET_QUIC_QUIC_RECEIVED_PACKET_MANAGER_H_